Synchronverters With a Virtual Oscillator to Attenuate Power Oscillations

A virtual oscillator (VO) based frequency-locked loop (FLL) is proposed to estimate the grid frequency
${\omega }_{g}$
and added to the control algorithm of a virtual synchronous machine (VSM) in order to better dampen oscillations in a power system comprising VSMs. The VO present in the virtual capacitor is used to estimate the ripple frequency. Similarly, a very simple but effective approximation is proposed, which features first-order dynamics instead of second-order in the conventional FLL. The change of VSM is to add a VO to offer a local friction-damping torque. The effect of the damping torque on the rotor of a VSM is similar to the presence of local friction damping on the same axis. Assumed that the damping torque is proportional to the frequency difference of
$\omega - \omega _{g}$
. Derive the damping torque
$T_{\mathrm{ vo}}$
based on the VO from the existing state variables of the fourth-order VSM model and its terminal voltages. Simulations and experiments verify the effectiveness of the proposed method in power oscillations damping.